High energy lasers and electrosurgical systems are becoming more common tools in surgery with a large variety of uses. When used in surgery, the laser beam or electrocautery knife vaporizes the tissue that it contacts, forming smoke. The smoke consists of particles that may include small amounts of liquid, bacteria, viruses, and any other by-product that may be generated during surgery. The smoke may restrict the field of view of the surgeon and may be potentially harmful to those who are exposed to it. The National Institute for Occupational Safety and Health has published a report at the request of a group of surgeons from Bryn Mawr Hospital (HETA-B5-l26-l932) recommending that ventilation controls must be used to minimize acute health effects and reduce the potential for long range chronic disorders that result from exposure to surgical smoke. Therefore, the smoke must be removed from the surgery site and contained in a safe manner.
The most common means for removal and containment of the smoke and surgery by-products is a suction system. The smoke and surgery by-products are transported through a flexible hose to a filter contained in a housing or canister where it is stopped. The suction system usually consists of three parts: a vacuum source, a collection system, and a filter.
The vacuum source applies a negative pressure to the collection system which facilitates suction of the smoke and surgery by-products from the surgery site into the collection system. The collection system is a reservoir in the form of housing or canister that collects the smoke and surgery by-products stopped by the filter. A collection system is described as a suction canister in the U.S. Pat. No. 4,487,606. The filter is intended to vent air while preventing the passage of particles including liquids and/or bacteria so that the suction system can keep the surgery site clear.
The majority of the smoke filters on the market contain multiple layers because a single layer would quickly clog and shut down the vacuum system since the collected smoke is heavily laden with particles. The use of a laser or electrocautery knife can produce a considerable amount of smoke. Therefore, filters used in laser and electrocautery surgery contain several layers because of the excessive particle matter they are required to filter. A smoke filter may consist of the following layers or elements; a prefilter layer to accept some of the particle load, a spacer or separator layer to prevent prefilter migration, charcoal to absorb odors, a final filter layer to remove and control the remaining particles that were passed by the prefilter layer and other layers that may be needed for backing, support, or adhesion. Multi-layer smoke filters to remove smoke produced during laser or electrocautery surgery are described in U.S. Pat. No. 4,619,672 and U.S. Pat. No. 4,487,606. Each layer has an important function in maintaining the service life of the filter. The filter materials must be chosen and constructed carefully to insure the prevention of harmful or nuisance substances from entering into the vacuum source. A well designed carefully constructed smoke filter can provide a safe, reliable and economical means of controlling the smoke particles and other liquids generated during laser and electrocautery surgery from entering into the suction system or outside environment.
The construction and selection of materials for a smoke filter must take into account the final application; the final application will determine what physical properties (air flow, filtration efficiency, water intrusion pressure etc.) are needed for the application. For example, some smoke filters are found in suction devices which are used for laser surgery and electrosurgery and are required to remove and contain large volumes of liquids. In these applications where large volumes of liquids are being collected, a need for controlling the overflow has been recognized. As described in the U.S. Pat. No. 4,487,606, the smoke filter functions as a filter to allow passage of air while controlling particle matter and as a valve to prevent liquid overflow by shutting down the vacuum system when the liquid in the collection system rises to cover the smoke filter. The filter element layer must have sufficiently low surface free energy and small pore structure to prevent the passage of the liquid. A smoke filter of this type must be made from a hydrophobic material and have the physical properties that allow acceptable air flow and prevent liquid passage under applied vacuum.
The selection of the materials for a smoke filter is sometimes complicated by the incompatibility of one or more of the layers. In the early development of smoke filters, three layer constructions consisted of a fiberglass prefilter layer, a microporous polytetrafluoroethylene (PTFE) membrane layer and a nonwoven support layer or backing. These smoke filters were tested for air permeability and water intrusion pressure (WIP). The testing revealed areas in which the WIP was greatly reduced, the areas of the filter in which the reduced WIP had occurred were examined using a Scanning Electron Microscope (SEM). The SEM revealed that glass fiber had penetrated through the microporous PTFE membrane layer and the support backing. The penetration of glass fiber violated the integrity of the microporous PTFE membrane layer and created holes in the membrane and backing that provided a path of lower resistance for the water to travel, thereby causing reduction in WIP. A damaged microporous polymeric membrane layer will not be able to control smoke particles, surgery by-products or prevent liquid overflow. A consequence of this damage to the microporous polymeric membrane, as detected by the reduction in the WIP, is that smoke particles and surgery by-products can enter the vacuum source and then into the hospital environment.
Present constructions of smoke filters do not address the problem of protecting the integrity of the microporous polymeric membrane layer. A means of protecting the microporous polymeric membrane layer from damaging prefiltration substrates is needed to insure that the passage of particles is prevented from entering the hospital environment. If the microporous polymeric membrane layer fails, the suction system can contaminate the hospital environment causing expensive cleaning up of the system or possible illness. Therefore, this invention is directed to a means of protecting the integrity of the microporous polymeric membrane so that it can function as it was intended: to control particle matter, prevent liquid overflow and maintain acceptable airflow. This invention may also be useful for any application where a filtration membrane requires protection from a damaging substrate without a large reduction in the air permeability of the membrane.